Electronic article surveillance (“EAS”) systems are detection systems that allow the identification of a marker or tag within a given detection zone. EAS systems have many uses, but most often they are used as security systems for preventing shoplifting in stores or removal of property in office buildings. EAS systems come in many different forms and make use of a number of different technologies.
A typical EAS system includes an electronic detection unit, tags and/or markers, and a detacher or deactivator. The detection units can, for example, be formed as pedestal units, buried under floors, mounted on walls, or hung from ceilings. The detection units are usually placed in high traffic areas, such as entrances and exits of stores or office buildings. The tags and/or markers have special characteristics and are specifically designed to be affixed to or embedded in merchandise or other objects sought to be protected. When an active tag passes through a tag detection zone, the EAS system sounds an alarm, a light is activated and/or some other suitable alert devices are activated to indicate the removal of the tag from the prescribed area.
Common EAS systems operate with these same general principles using either transceivers, which each transmit and receive, or a separate transmitter and receiver. Typically the transmitter is placed on one side of the detection zone and the receiver is placed on the opposite side of the detection zone. The transmitter produces a predetermined excitation signal in a tag detection zone. In the case of a retail store, this detection zone is usually formed at an exit. When an EAS tag enters the detection zone, the tag has a characteristic response to the excitation signal, which can be detected. For example, the tag may respond to the signal sent by the transmitter by using a simple semiconductor junction, a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating acousto-magnetic (“AM”) resonators. For example “AM” tags are devices that exhibit specific response properties when activated and deactivated. When activated, AM tags resonate and transmit a signal at a resonant frequency when stimulated by an interrogation signal at a particular frequency. The receiver subsequently detects this characteristic response. The properties of “deactivated” AM tags result in the inability to transmit a signal at the resonant frequency. By design, the characteristic response of the tag is distinctive and not likely to be created by natural circumstances.
A consideration in connection with the design and use of such EAS systems is to minimize the occurrence of false alarms which could either cause embarrassment to customers of an EAS system user, e.g., a retail store, or produce annoying and disruptive alarm signals when no one is passing through the store's EAS system. There are various types of false alarm signals including a “false” alarm that occurs when a shopper passes through the EAS system without possessing any tag-bearing or protected merchandise, but an alarm is nevertheless sounded. Yet another more specific type of false alarm signal is the “merchandise” alarm, which occurs when a shopper carries non-protected merchandise through the EAS system which nevertheless exhibits the characteristics of an active tag. Examples of this are items such as extension cords and cables, foldable chairs, and other coiled metal objects that are capable of resonance in the presence of the electromagnetic field of an EAS system. Another specific type of false alarm signal is the “phantom” alarm, which occurs when an EAS system sounds an alarm responsive to the detection of an “ambient” signal, generally when there is no one passing through the EAS system. Examples are false alarm signals produced by tag-bearing merchandise placed on display near enough to the EAS system to accidentally cause an alarm condition or when tag-bearing merchandise is temporarily introduced into the detection zone but does not exit the retail space.
Another type of false alarm occurs with there is a failure to deactivate (“FTD”) event which occurs when a tag is improperly deactivated or “wounded”. A tag is “wounded” when the tag has not been completely deactivated but remains in a state where the tag is on the threshold of being a valid tag. For example, in current EAS systems, when AM tags (also referred to herein as “labels”) are properly deactivated one can expect the frequency of the label as detected by the system receiver to be approximately 59.3 kHz. The AM detector's frequency criterion rejects detection of labels with frequencies greater than 58.6 kHz. In some cases a partially or inappropriately deactivated labels may have a frequency less than 58.6 kHz, in which case the system will unintentionally alarm (false alarm).
What is needed is a method and system that can be used to reduce or eliminate false alarms in EAS system detection zones especially when tags have not been properly deactivated.